Sn-plated copper alloy strips have been used as electrically conductive material for a terminal, connector, relay, switch, and the like. After Sn-plated copper alloy strips are molded into electronic components, they will be repeatedly subjected to stress equal to or less than their elastic limit caused by, for example, insertion and pullout of the connecter, on-off action of the switch or relay, and vibration. Therefore, an Sn-plated copper strip, which is used in a connector, terminal, relay, switch and the like, is required to have good fatigue characteristics. In recent years, as electronic components have become thinner and smaller, the stress repeatedly imposed on metallic elements is likely to increase. In addition, the requirement for the reliability and durability of electronic components has also become severer. Therefore, the need for improved fatigue characteristics is growing.
In response, various technologies for improving the fatigue characteristics of copper alloy have been disclosed in the past (e.g., Japanese unexamined patent publication No. 2004-218084).